I once booked a plane ticket from my home town airport to another country. The purchase notification said something like "PVA" instead of "POV". I looked it up and turned out, the newly built airport that had this exact code was about to open. In a week or so, so I assumed that I'm indeed flying from the new one and forgot about it. The purchase was made through a booking aggregator similar to Expedia. On the day of…
Yeah they generally have the capability to prevent that auto cancellation of your segments (within a certain time frame) but in this case unfortunately they were unwilling or it was too late to catch it.
It's generally to protect revenue because buying A-B-C instead of B-C can be cheaper, and hoards of people used to just segments to save money. So they just assume everyone is trying to cheat them.